For purposes of this application and the claims herein, the term "backpropagation" shall be defined to mean that operation that is the inverse or approximate inverse of a forward propagation process. The term "filtered backpropagation technique" shall be defined to describe any diffraction tomographic technique for the partial or complete reconstruction of an object where a filtered real or complex amplitude and/or filtered real or complex phase of a wave is backpropagated into the object space; i.e., is propagated back into object space according to the inverse or approximate inverse of the way in which the wave was originally diffracted. The filtered backpropagation technique is usually implemented in the form of a convolution of filters. For purposes of brevity, such an implementation will identically be called the filtered backpropagation technique. A "backpropagation filter" shall be defined to describe that filter of the filtered backpropagation technique which accounts for diffraction in the backpropagation of the phase; e.g. in ultrasound diffraction tomography, the filter of the filtered backpropagation technique which is not the standard X-ray tomographic filter (or a variation thereon). A "filtered backpropagation operation" shall be defined as any procedure which employs the filtered backpropagation technique. Also, for purposes of this application, one-dimensional fixed detector array shall be defined to include both an array of detectors on a fixed line, and one detector scanned over a fixed line, or any equivalent thereof. A two-dimensional fixed detector array shall include one detector scanned over a fixed plane, an array of detectors on a line scanned over a fixed plane, or a two-dimensional array of detectors on a fixed plane, or any equivalent thereof.
Further, for purposes of this application and claims herein, it should be understood that the waves of eneregy which propagate and diffract according to the invention include but are not limited to sonic or electromagnetic waves. The term "sonic wave" shall be interpreted as broadly as possible and shall be understood to include all elastic wave phenomena in liquid and solid materials including, but not limited to, acoutic, compressional, shear, and elastic waves. The term "acoutic wave" shall be interpreted herein to be the equivalent of "sonic wave". The term "electromagnetic wave" shall also be interpreted in its broadest sense and shall include, but not be limited to infrared rays, X-rays, and the class known as "optics".
This invention relates to systems and methods for reconstructing acoustic and/or electromagnetic properties of two or three-dimensional objects using diffraction tomographic procedures wherein the detector array of the system is located on a plane or line fixed in space. An example of such a system is disclosed in copending Ser. No. 441,323 with regards to the geophysical diffraction tomography embodiments discussed therein. While systems and methods for geophysical diffraction tomography were described therein, and those disclosed systems and methods utilized a filtered backpropagation technique (as defined in Ser. No. 441,323 and identically defined herein), the filtered backpropagation technique and the preprocessing disclosed herein should be preferable to those previously disclosed.
While certain standard conventional ultrasound imaging systems employ fixed detection arrays, those systems do not incorporate a backpropagation filter or a filtered backpropagation technique. Conversely, while in copending Ser. No. 441,323, there is a detailed description of a filtered backpropagation technique, there is no detailed discussion on how to tailor the backpropagation filter and filtered backpropagation technique for use with a fixed detector array for ultrasound diffraction tomography, for either two-dimensional or three-dimensional objects. The advantages of a fixed detector array reconstruction system are numerous and desirable, but until now have not been obtained in a high-resolution ultrasonic tomography system.
The use of backscatter information in imaging is also known. Standard pulse echo systems often use the same transducer arrays as both transmitters and receivers. (See, for example, U.S. Pat. No. 4,258,576 to Vilkomerson et al., U.S. Pat. No. 4,381,787 to Hottinger and U.S. Pat. No. 4,248,091 to Hashiguchi.) Again, however, there has been no disclosure in either Ser. No. 441,323 or in the prior art which tailors the use of a filtered backpropagation technique to optimize it for backscatter information. Those skilled in the art will appreciate that the backscatter situation is just a special case of the broader fixed detector array embodiment because in backscatter, the detector array is fixed to be along the same line or plane as the sources. Nevertheless, the filtered backpropagation technique must be altered in some backscatter situations to optimally process the backscatter information.